This invention relates to the field of instrumentation. More particularly, this invention relates to improved data output from an electron microscope.
In the integrated circuit industry, electron microscopes are used to review integrated circuit components for a variety of purposes, including critical dimensions and component defects. The quality of the finished integrated circuit tends to be highly dependent on the accurate detection of imperfections by the electron microscope. Thus, it is very important to ensure that the data received from the electron microscope is complete and useable.
Typically, an electron microscope creates a still image at a single set of parameters, such as landing energy, angle of incidence, zoom factor, position of sample, focal plane, and charge accumulation. A user reviews the image produced by the electron microscope to detect any imperfections in the integrated circuit components.
There are several disadvantages to the typical method. The data taken at a single set of conditions may not contain the desired data. For example, the image may not show a defect that is obscured from view at all but a narrow range of angles. Further, a two dimensional still image produced by the electron microscope does not allow for three dimensional reconstructions of the structures in the samples. Also, when data is stored for later use or communicated to other users, such other users often cannot determine what the imaged data is showing. Such users cannot zoom out to obtain a larger image, pan to other portions of the component, change the image""s focal plane, or adjust the charge accumulation. Because it is often not possible to later recreate the image as it was taken with a specific set of parameters, the opportunity to detect certain defects or to otherwise adequately analyze the sample may be lost.
What is needed, therefore, is a system to improve the usability and completeness of data gathered from an electron microscope.
The above and other needs are met by an apparatus for recording a series of images of a sample over a period of time while varying at least one image parameter. An electron microscope captures images of the sample and also varies the at least one image parameter. A controller triggers the electron microscope to sense multiple images of the sample over the period of time and also controls the electron microscope to vary the at least one image parameter over the period of time. An image recorder receives the sensed multiple images and also stores the sensed multiple images as the series of images. A display unit displays the series of images.
In this manner, the system described herein provides numerous advantages relating to the data output from an electron microscope. The system enables higher confidence in the accuracy and completeness of data and allows a user to locate defects that would be obscured from view at a small set of parameters. When the sample images are communicated to others or reviewed at a later time, the user will not have to recreate the data, because the desired information is contained in the series of images. Further, if a desired feature of the sample cannot be identified in one or more of the images in the series sensed at a given set of parameters, the system allows a user to view images from the series sensed at a different set of parameters, so that the desired feature is easier to identify. By varying the image parameters used in the sample images during the review, a user can obtain a more complete recreation of the reviewed area of the integrated circuit. This improved confidence and data usability enables more complete and accurate review of critical dimensions and defects, leading to higher yield in the manufacture of integrated circuits.
In various preferred embodiments, the imaging tool is an electron microscope, and most preferably a scanning electron microscope. The display of the series of images is preferably one of a motion picture in free running mode, a motion picture in manually controlled mode, a three dimensional reconstruction, and a simultaneous display at least a portion of the series of images as a super resolution image. The image parameters varied by the controller preferably include both imaging tool parameters and sample parameters. Imaging tool parameters include those parameters which affect the imaging tool, such as landing energy, zoom factor, focal plane, energy filter setting, angle of incidence by changing the beam angle, and charge accumulation. Sample parameters include those parameters which affect the sample, such as angle of incidence by changing the sample angle, and position of sample.